Automated fiber placement machines are widely used to manufacture parts, components and structures from composite material. The materials used in automated fiber placement are typically composed of longitudinal fibers and resin consolidated into tapes, or thin strips, commonly known as “tows.” Individual tapes or tows are manipulated by the fiber placement machine to form a band of material that is deposited onto a tool. Parts are built up layer-by-layer, with tapes or tows of composite material, with the angle at which each layer “ply” is laid onto the tool being precisely determined by the fiber placement machine.
Automated fiber placement enables the construction of complex composite structures having steered or curvilinear fiber paths. This method of producing composite structures is more cost effective than manual methods. It provides an improved structural efficiency due to its ability to orient the fibers along local internal loads paths, which potentially results in lighter structures and lower costs than in structures made by other production methods.
During the fiber placement process, it is sometimes necessary to cut and stop the feed of individual tows, thus removing them from the band of material, in order to reduce the width of the band so that it may be placed onto the surface of the mold or tool in a manner that precludes having excessive gaps between successive bands of material, or having the edges of successive bands of material overlap one another. In similar fashion, it is often desirable to add tows to the band in order to increase its width, at various stages of the automated fiber placement process, in order to facilitate manufacture of the composite structure. The process of removing or adding tows is commonly referred to “cut and add” (cut/add).
Automated fiber placement machines are capable of depositing material onto a tool surface at high feed-rates, of, for example, 1200 inches/minute or higher. For maximizing productivity, it is desirable to operate an automated fiber placement machine at such high feed-rates throughout the fabrication of a composite structure. It is highly desirable, therefore, that automated fiber placement machines be capable of modifying the width of the band of material being applied without stopping, or slowing down, the machine to cut or add tows to the material band. In the vernacular of the automated fiber placement industry, it is highly desirable that automated fiber placement machines be capable of cutting or adding tows “on-the-fly.”
In order to cut or add tows to the material band on-the-fly, the cut/add process must take place in real time. The components of the automated fiber placement machine which perform and control the cut/add process are incapable of instantaneously cutting or adding a tow to the band of material, due to inherent and unavoidable lag times or other latencies in the operation of mechanical, hydraulic, pneumatic, or electrical actuation and control components of the automated fiber placement machine. These unavoidable and inherent latencies result in the end of a cut or added tow often being positioned well outside of the tolerances required for constructing the composite structure where on-the-fly cut/add is attempted at full operating speed using prior fiber placement machines.
The problems described above, with regard to cut/add operations, are also encountered in other operations performed at high-speed on-the-fly during fabrication of a composite structure, such as changing tension, temperature, or pressure applied on a tow or the material band during automated fiber placement.
Commonly assigned U.S. patent application Ser. No. 11/111,498, filed Apr. 21, 2005, entitled, PERFORMING HIGH SPEED EVENTS “ON-THE-FLY” DURING FABRICATION OF A COMPOSITE STRUCTURE BY AUTOMATED FIBER PLACEMENT, which is incorporated herein in its entirety by reference, provides a description of various processes performed on-the-fly during an automated fiber placement process.
The invention provides an improved method and apparatus for performing a high-speed event in an automated fiber placement process by initiating the high-speed event prior to the fiber placement head reaching a location along a tool path of the fiber placement head at which it is desired to have the high-speed event completed.
In one form of the invention, a method is provided for performing a high-speed event in an automated fiber placement process using a fiber placement head of a fiber placement machine for fabricating a composite structure. The method includes determining a time-based tool path for the fiber placement head during fabrication of the composite part, with the time-based tool path including a completion location of the fiber placement head along the tool path at which it is desired to have completed the high-speed event. An initiation location of the fiber placement head along the tool path is also determined. The initiation location is disposed sufficiently in advance of the completion location, along the tool path, such that initiation of the desired high-speed event at the initiation location of the fiber placement head results in completion of the desired high-speed event substantially at the completion location of the fiber placement head.
A method, according to the invention, may further include initiating the desired high-speed event substantially at the initiation location of the fiber placement head along the tool path. The high-speed event may also be performed according to a desired process.
The invention may also include determining a latency value for the fiber placement machine to perform the high-speed event, with the latency value being used for determining the initiation location of the fiber placement head along the tool path.
The invention may also take the form of an apparatus or method for determining and tabulating a desired position during fabrication of the composite structure for starting or stopping the desired high-speed event, determining and tabulating a completion location of the fiber placement head along the tool path for each desired position for starting or stopping the high-speed event, and determining and tabulating an initiation location of the fiber placement head for starting or stopping at least one of the high-speed events. A method or apparatus, according to the invention, may further include provision for determining and tabulating latency values for the fiber placement machine to perform the high-speed event, and using the tabulated latency values for determining the initiation location of the fiber placement head along the tool path.
The invention may also take the form of a method, apparatus, or software including a computer readable medium having computer executable instructions for practicing the invention.
Although apparatuses and methods built and operated in accordance with the Assignee's commonly assigned U.S. patent application Ser. No. 11/111,498, provides significant improvements in the accuracy with which tows can be added during high-speed fiber placement, it has been found that the configuration and operation of prior add roller apparatuses, used for initiating the feeding of tows to be added, can be a limiting factor, due to inherent rotational inertias, and drag, which must be overcome in the prior apparatuses, before the tow to be added can be brought up to the same speed as other tows in the ply.
In order to effectively add plys on-the-fly, it is necessary that the added ply be brought up to a speed matching the speed at which existing plys are being laid down by the fiber placement head. If this is not accomplished, the added ply will tend to bunch up or be improperly placed.
As shown in FIGS. 1 and 2, in prior add roll apparatuses 10, when it is desired to add a tow 12 to a band of tows (not shown) being laid down by a fiber placement head (not shown), and add roller 14 is forced toward a feed roller 16, to thereby clamp the added tow 12 between the add roller 14 and a driving surface 18 of the feed roller 16, in such a manner that the tow 12 is fed from a spool 20 to the fiber placement head. Each of the tows in the band of tows being laid down by the fiber placement head has associated with it a respective add roller 14, with the feed roller 16 generally extending completely across the band of tows, and serving as a common drive source for feeding the tows in the band out to the fiber placement head.
As shown in FIG. 3, prior add roller apparatuses and methods have utilized add rollers 14 having an add roller width 22 which is narrower than the tow width 24.
As a result of the add roller width 22 being narrower than the tow width 24, the add roller 14 was never brought into direct contact with the rotating feed surface 18 of the feed roller 16 directly. This results in an inefficient arrangement for transferring rotational force through the added tow 12 to the add roller 14, in order to drive the add roller 14 up to a speed matching the add rollers of other plys already being laid down at high speed by the fiber placement head. The time required to spin the add roller up to the same speed as other add rollers, and the transferred rotational energy which must be diverted through the added tow 12 for bringing the add roller 14 up to speed creates an undesired delay, and limits efficiency and effectiveness of the process of adding the tow 12 to the band of tows being laid down by the fiber placement head.
It is desirable, therefore, to provide an improved method and/or apparatus for automatically ensuring that an added tow is brought up to the same speed as existing tows passing over a feed roller of a fiber placement head, more quickly, and with greater efficiency and effectiveness than has heretofore been possible with prior add roller apparatuses and methods. It is also desirable, that such an improved method and apparatus, be usable in apparatuses and methods such as those laid out in commonly assigned U.S. patent application Ser. No. 11/111,498, and also in add roller apparatuses and methods not utilizing the improved methods and apparatuses of commonly assigned U.S. patent application Ser. No. 11/111,498.